1. Field of the Invention
The present invention relates to an apparatus and a method for driving a liquid crystal display device, and more particularly, to an apparatus and a method for driving a lamp of a liquid crystal display device that is capable of controlling a partial brightness and a color character.
2. Description of the Related Art
In general, a liquid crystal display (hereinafter, LCD) has a trend that its application scope has been gradually widened due to its lightness, its thinness, and its low power consumption. In accordance with such a trend, the LCD is used in an office automation device, an audio/video device and the like. The LCD adjusts the transmittance quantity of a light beam in accordance with an image signal applied to a matrix of a plurality of control switches to thereby display desired pictures on a screen.
Since the LCD is not a spontaneous light-emitting display device, the LCD device needs a backlight unit as a light source. There are two types of the backlight unit for the LCD, i.e., a direct-below type and a light guide plate type. In the direct-below type, several lamps are arranged in the plane. And, a diffusion panel is installed between the lamps and the liquid crystal display panel to fixedly keep the distance between the liquid crystal display panel and the lamps. In the light guide plate type, a lamp is installed in the outer part of the flat panel, and the light from the lamp is incident on the entire surface of the liquid crystal display panel by using a transparent light guide plate.
Referring to FIGS. 1 and 2, the LCD adopting the related art direct-below type backlight includes a liquid crystal display panel 2 to display a picture, and a direct-below type backlight unit to irradiate a uniform light onto the liquid crystal display panel 2.
In the liquid crystal display panel 2, liquid crystal cells are arranged between an upper substrate and a lower substrate in such a manner of an active matrix type, and a common electrode and pixel electrodes to apply an electric field to each of the liquid crystal cells are provided. Generally, the pixel electrode is formed on the lower substrate, i.e., a thin film transistor substrate, for each liquid crystal cell. On the other hand, the common electrode is formed to be integrated with the front surface of the upper substrate. Each of the pixel electrodes is connected to a thin film transistor that is used as a switching device. The pixel electrode drives the liquid crystal cell along with the common electrode in accordance with a data signal supplied through the thin film transistor, thereby displaying a picture corresponding to a video signal.
The direct-below type backlight unit includes a plurality of lamps 36 to generate light, a lamp housing (or a lamp holding container of the direct-below type backlight unit) 34 located at the lower part of the lamps 36, a diffusion plate 12 covering the lamp housing 34, and optical sheets 10 located on the diffusion plate 12.
Each of the lamps 36 includes a glass tube, an inert gas in the inside of the glass tube, and a cathode and an anode installed at both ends of the glass tube. The inside of the glass tube is charged with the inert gas, and the phosphorus is spread over the inner wall of the glass tube.
In each of the lamps 36, if an AC waveform of high voltage is applied to a high voltage electrode and a low voltage electrode from an inverter (not shown), electrons are emitted from the low voltage electrode L to collide with the inert gas in the glass tube, thus the amount of electrons is increased in geometrical progression. The increased electrons cause electric current to flow in the inside of the glass tube, so that the inert gas is excited by the electrons to emit ultraviolet ray. The ultraviolet ray collides with a luminous phosphorus spread over the inner wall of the glass tube to emit visible ray. At this moment, the AC waveform of high voltage is continuously supplied to the lamps 36 so that the lamps are always turned on.
In this way, the lamps 36 are arranged in parallel in the lamp housing 34.
The lamp housing 34 prevents the light leakage of the visible ray emitted from each of the lamps 36 and reflects the visible ray, progressing to the side surface and the rear surface of the lamps 36, to the front surface, i.e., toward the diffusion plate 12, thereby improving the efficiency of the light generated at the lamps 36.
The diffusion plate 12 enables the light emitted from the lamps 36 to progress toward the liquid crystal display panel 2 and to be incident at an angle of a wide range. The diffusion plate 12 is a light diffusion member that is coated on both sides of the film which is composed of transparent resin.
The optical sheets 10 narrow the viewing angle of the light coming out of the diffusion plate 12, thus it is possible that the front brightness of the liquid crystal display device is improved and its power consumption is reduced.
A reflection sheet 14 is arranged between the lamps 36 and the bottom area of the lamp housing 34 to reflect the light generated from the lamps 36 so as to irradiate it in the direction of the liquid crystal display panel 2, thereby improving the efficiency of light.
In this way, the related art LCD generates a uniform light by use of the lamps 36 arranged in the lamp housing 34 to irradiate it to the liquid crystal display panel 2, thereby displaying the desired picture. However, the related art LCD has disadvantages in that it needs to have the lamps turned on continuously, whereby its power consumption is large and a partial peak brightness cannot be realized. The peak brightness is a brightness that occurs when a designated part on the liquid crystal display panel 2 is operated to be instantly brightened in order to display a picture like an explosion or a flash on the liquid crystal display panel 2.